Semiconductor manufacturers face an everlasting quest to comply with Moore's Law. They constantly strive to continually decrease feature sizes, such as active and passive devices, interconnecting wire widths and thicknesses and power consumption. In addition, tremendous effort is made to increase device density, wire density and operating frequencies.
These challenges have led the semiconductor industry to devise several breakthroughs for manufacturing different logic circuits, such as microprocessors and random access memory chips. Currently, the industry faces the challenge to come up with better interconnects and dielectrics to remedy the bottleneck for device functionality. For the interconnects, manufacturers utilize metals with better electrical and thermal conductivity. For example, copper wiring in place of those based on aluminum and aluminum alloys. Copper, which has a lower resistivity, greater thermal conductivity and a greater electro-migration lifetime eliminates many of the problems associated with aluminum and is more suitable for use in low-power, low-voltage and high speed applications. However, there are difficulties with fabricating copper interconnects. Because of the lack of volatile copper compounds, copper could not be patterned by the previous techniques of photoresist masking and plasma etching that had been used with great success with aluminum. Moreover, the copper can diffuse through many dielectric materials complicating the fabrication process of copper wiring. The manufacturers had to invent a radically new patterning process, which lead to the introduction of the so called damascene and dual damascene processes. During a damascene process, dielectrics are patterned using traditional methods to define trenches and vias. Then copper is deposited using electroplating and the excess is subsequently removed by chemical mechanical planarization.
Another approach is to improve the functionality of devices was the introduction of low-K dielectrics. In this type of dielectrics the dielectric constant reduction is achieved by reducing polarizability, by reducing density, or by introducing porosity, or any combination thereof. This poses further integration challenges to manufacturers, since the reduction of the dielectric constant is usually achieved at the expense of useful material properties required for metallic interconnect fabrication.
Therefore, there is a need for improved methods of fabrication of metallic interconnect wiring in low-K dielectrics, which resolve certain challenges faced by the semiconductor industry.
Corresponding numerals and symbols in the different figures generally refer to corresponding parts unless otherwise indicated. The figures are drawn to clearly illustrate the relevant aspects of the embodiments and are not necessarily drawn to scale.